I need running backpack help!

kit_katty

I bought a running backpack many months ago and have had no problems with it until now, this is the first summer that I've run with it and it's started to chafe the sides of my neck.

Does anyone have any ideas on how to prevent this? It's not just a hydration pack, I run to and from work every other day, so I have some stuff in it, though today when the worse chafing happened my pack was actually rather light...

Any help would be appreciate it! Thanks!